SQLDataReader-Retrieving multiple rows with same project id and rating

I am fairly rustic in VB.NET using the SQLData Reader object and would appreciate any help. I am actually considering an inquiry on how to retrieve the number of rows of project id (i.e) those project that have the same project id and rating(i.e) feedback given by users on submission of a click (Submit Button designed in GUI) ... The insert query writes the data into ProjectRating table and that table is linked with the Project table...However I need to be able to update the Average Rating row of Project table.

When a user clicks on submit button for that Project id the rating is added and the number of raters is kept track . So for every user who gives the rating through combobox rating combobox the rating value is added to the previous rating value (How to go by this??No Ideas..Anybody can help in that) and then divided by number of raters... This in way is updated in the Project table...and the value is computed in the averagerating column...

How to go by this... I would like a small sample code to give me a fair insight on using the SQLDataReader... like in the above case